Swift X-ray and ultraviolet observations of the shortest orbital period double-degenerate system RX J0806.3+1527 (HM Cnc)
Abstract
The system RX J0806.3+1527 (HM Cnc) is a pulsating X-ray source with 100 per cent modulation on a period of 321.5 s (5.4 min). This period reflects the orbital motion of a close binary consisting of two interacting white dwarfs. Here we present a series of simultaneous X-ray (0.2-10 keV) and near-ultraviolet (2600 Å and 1928 Å) observations that were carried out with the Swift satellite. In the near-ultraviolet, the counterpart of RX J0806.3+1527 was detected at flux densities consistent with a blackbody with a temperature of (27 ± 8) × 103 K. We found that the emission at 2600 Å is modulated at the 321.5-s period with the peak ahead of the X-ray one by 0.28 ± 0.02 cycles and is coincident within ± 0.05 cycles with the optical. This phase-shift measurement confirms that the X-ray hot spot (located on the primary white dwarf) is at about 80°-100° from the direction that connects the two white dwarfs. Albeit at lower significance, the 321.5-s signature is also present in the 1928-Å data; at this wavelength, however, the pulse peak is better aligned with that observed at X-rays. We use the constraints on the source luminosity and the geometry of the emitting regions to discuss the merits and limits of the main models for RX J0806.3+1527.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- January 2014
- DOI:
- 10.1051/0004-6361/201322719
- arXiv:
- arXiv:1311.6973
- Bibcode:
- 2014A&A...561A.117E
- Keywords:
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- stars: individual: RX J0806.3+1527 (HM Cnc);
- X-rays: binaries;
- ultraviolet: stars;
- binaries: close;
- white dwarfs;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Minor changes to match final version (Astronomy &